usbip: vhci_sysfs: fix potential Spectre v1

pdev_nr and rhport can be controlled by user-space, hence leading to a potential exploitation of the Spectre variant 1 vulnerability.

This issue was detected with the help of Smatch:
drivers/usb/usbip/vhci_sysfs.c:238 detach_store() warn: potential spectre issue 'vhcis' drivers/usb/usbip/vhci_sysfs.c:328 attach_store() warn: potential spectre issue 'vhcis' drivers/usb/usbip/vhci_sysfs.c:338 attach_store() warn: potential spectre issue 'vhci->vhci_hcd_ss->vdev' drivers/usb/usbip/vhci_sysfs.c:340 attach_store() warn: potential spectre issue 'vhci->vhci_hcd_hs->vdev'

Fix this by sanitizing pdev_nr and rhport before using them to index vhcis and vhci->vhci_hcd_ss->vdev respectively.

Notice that given that speculation windows are large, the policy is to kill the speculation on the first load and not worry if it can be completed with a dependent load/store [1].

[1] https://marc.info/?l=linux-kernel&m=152449131114778&w=2

Cc [email protected]

Signed-off-by Gustavo A. R. Silva <[email protected]>

---
Changes in v3:
- Pass the addresses of pdev_nr and rhport into valid_port and valid_args.

Changes in v2:
- Place the barriers into valid_port.

 drivers/usb/usbip/vhci_sysfs.c | 24 ++++++++++++++++--------
 1 file changed, 16 insertions(+), 8 deletions(-)

drivers/usb/usbip/vhci_sysfs.c +15 -7

index 4880838..be37aec 100644
@@ -10,6 +10,9 @@
 #include <linux/platform_device.h>
 #include <linux/slab.h>
 
+/* Hardening for Spectre-v1 */
+#include <linux/nospec.h>
+
 #include "usbip_common.h"
 #include "vhci.h"
 

@@ -205,16 +208,20 @@ static int vhci_port_disconnect(struct vhci_hcd *vhci_hcd, __u32 rhport)
 	return 0;
 }
 
-static int valid_port(__u32 pdev_nr, __u32 rhport)
+static int valid_port(__u32 *pdev_nr, __u32 *rhport)
 {
-	if (pdev_nr >= vhci_num_controllers) {
-		pr_err("pdev %u\n", pdev_nr);
+	if (*pdev_nr >= vhci_num_controllers) {
+		pr_err("pdev %u\n", *pdev_nr);
 		return 0;
 	}
-	if (rhport >= VHCI_HC_PORTS) {
-		pr_err("rhport %u\n", rhport);
+	*pdev_nr = array_index_nospec(*pdev_nr, vhci_num_controllers);
+
+	if (*rhport >= VHCI_HC_PORTS) {
+		pr_err("rhport %u\n", *rhport);
 		return 0;
 	}
+	*rhport = array_index_nospec(*rhport, VHCI_HC_PORTS);
+
 	return 1;
 }
 

@@ -232,7 +239,7 @@ static ssize_t detach_store(struct device *dev, struct device_attribute *attr,
 	pdev_nr = port_to_pdev_nr(port);
 	rhport = port_to_rhport(port);
 
-	if (!valid_port(pdev_nr, rhport))
+	if (!valid_port(&pdev_nr, &rhport))
 		return -EINVAL;
 
 	hcd = platform_get_drvdata(vhcis[pdev_nr].pdev);

@@ -258,7 +265,8 @@ static ssize_t detach_store(struct device *dev, struct device_attribute *attr,
 }
 static DEVICE_ATTR_WO(detach);
 
-static int valid_args(__u32 pdev_nr, __u32 rhport, enum usb_device_speed speed)
+static int valid_args(__u32 *pdev_nr, __u32 *rhport,
+		      enum usb_device_speed speed)
 {
 	if (!valid_port(pdev_nr, rhport)) {
 		return 0;

Quoted 98 lines · Gustavo A. R. Silva

pdev_nr and rhport can be controlled by user-space, hence leading to a potential exploitation of the Spectre variant 1 vulnerability.

This issue was detected with the help of Smatch:
drivers/usb/usbip/vhci_sysfs.c:238 detach_store() warn: potential spectre issue 'vhcis' drivers/usb/usbip/vhci_sysfs.c:328 attach_store() warn: potential spectre issue 'vhcis' drivers/usb/usbip/vhci_sysfs.c:338 attach_store() warn: potential spectre issue 'vhci->vhci_hcd_ss->vdev' drivers/usb/usbip/vhci_sysfs.c:340 attach_store() warn: potential spectre issue 'vhci->vhci_hcd_hs->vdev'

Fix this by sanitizing pdev_nr and rhport before using them to index vhcis and vhci->vhci_hcd_ss->vdev respectively.

Notice that given that speculation windows are large, the policy is to kill the speculation on the first load and not worry if it can be completed with a dependent load/store [1].

[1] https://marc.info/?l=linux-kernel&m=152449131114778&w=2

Cc [email protected]

Signed-off-by Gustavo A. R. Silva <[email protected]>

---
Changes in v3:
- Pass the addresses of pdev_nr and rhport into valid_port and valid_args.

Changes in v2:
- Place the barriers into valid_port.

  drivers/usb/usbip/vhci_sysfs.c | 24 ++++++++++++++++--------
  1 file changed, 16 insertions(+), 8 deletions(-)

drivers/usb/usbip/vhci_sysfs.c +16 -8

index 4880838..be37aec 100644
@@ -10,6 +10,9 @@
  #include <linux/platform_device.h>
  #include <linux/slab.h>
 
+/* Hardening for Spectre-v1 */
+#include <linux/nospec.h>
+
  #include "usbip_common.h"
  #include "vhci.h"
 

@@ -205,16 +208,20 @@ static int vhci_port_disconnect(struct vhci_hcd *vhci_hcd, __u32 rhport)
  	return 0;
  }
 
-static int valid_port(__u32 pdev_nr, __u32 rhport)
+static int valid_port(__u32 *pdev_nr, __u32 *rhport)
  {
-	if (pdev_nr >= vhci_num_controllers) {
-		pr_err("pdev %u\n", pdev_nr);
+	if (*pdev_nr >= vhci_num_controllers) {
+		pr_err("pdev %u\n", *pdev_nr);
  		return 0;
  	}
-	if (rhport >= VHCI_HC_PORTS) {
-		pr_err("rhport %u\n", rhport);
+	*pdev_nr = array_index_nospec(*pdev_nr, vhci_num_controllers);
+
+	if (*rhport >= VHCI_HC_PORTS) {
+		pr_err("rhport %u\n", *rhport);
  		return 0;
  	}
+	*rhport = array_index_nospec(*rhport, VHCI_HC_PORTS);
+
  	return 1;
  }
 

@@ -232,7 +239,7 @@ static ssize_t detach_store(struct device *dev, struct device_attribute *attr,
  	pdev_nr = port_to_pdev_nr(port);
  	rhport = port_to_rhport(port);
 
-	if (!valid_port(pdev_nr, rhport))
+	if (!valid_port(&pdev_nr, &rhport))
  		return -EINVAL;
 
  	hcd = platform_get_drvdata(vhcis[pdev_nr].pdev);

@@ -258,7 +265,8 @@ static ssize_t detach_store(struct device *dev, struct device_attribute *attr,
  }
  static DEVICE_ATTR_WO(detach);
 
-static int valid_args(__u32 pdev_nr, __u32 rhport, enum usb_device_speed speed)
+static int valid_args(__u32 *pdev_nr, __u32 *rhport,
+		      enum usb_device_speed speed)
  {
  	if (!valid_port(pdev_nr, rhport)) {
  		return 0;

@@ -322,7 +330,7 @@ static ssize_t attach_store(struct device *dev, struct device_attribute *attr,
  			     sockfd, devid, speed);
 
  	/* check received parameters */
-	if (!valid_args(pdev_nr, rhport, speed))
+	if (!valid_args(&pdev_nr, &rhport, speed))
  		return -EINVAL;
 

drivers/usb/usbip/vhci_sysfs.c static ssize_t attach_store(struct device *dev, struct device_attribute *attr, · line 336

Quoted 2 lines

drivers/usb/usbip/vhci_sysfs.c +0 -0

  	hcd = platform_get_drvdata(vhcis[pdev_nr].pdev);

Looks good to me. Thanks for taking care of this.

Acked-by Shuah Khan (Samsung OSG) <[email protected]>